1. Field of the Invention
This invention is in the field of free piston gas generators and particularly the field of free piston gas generators fueled with char fuels such as coal or charcoal.
2. Description of the Prior Art
Prior art free piston gas generators comprise one or more air compressor pistons and cylinders, one or more power pistons and cylinders, one or more bounce pistons and cylinders, a diesel fuel supply and injection system and necessary air compressor valves, power piston intake and exhaust ports, etc. Usually an air compressor piston, a power piston and a bounce piston are assembled together as a single piece and two such pieces operate together, symmetrically about the diesel fuel combustion system, as a single free piston gas generator.
Such a diesel fueled free piston gas generator differs from a diesel fueled internal combustion engine in the following ways:
a. No net shaft work output emerges from a free piston gas generator.
b. The cycle work of the free piston gas generator is fully absorbed internally to drive the air compressor.
c. The useful net output of a free piston gas generator is either the exhaust gas at pressure or this exhaust gas plus compressed air.
d. For a diesel fueled internal combustion engine the cycle work emerges as the useful net shaft work output, exhaust gas is not at high pressure, and compressed air is not usually delivered outside the engine.
Prior art diesel fueled free piston gas generators have been used as compressed air supply sources and as high pressure exhaust gas supply sources for driving gas turbine engines. References A, B and C describe various such prior art uses of diesel fueled free piston gas generators. These prior art free piston gas generators have seen only very limited use for driving gas turbine engines or as sources of high pressure exhaust gas principally for the following reasons:
a. The combination of a free piston gas generator and a gas turbine engine is more complex and less efficient, particularly at part load, than a diesel internal combustion engine.
b. These diesel fueled free piston gas generators cannot efficiently produce an exhaust gas which is a fuel gas.
c. These prior art free piston gas generators require use of a liquid fuel and these are now very expensive.
The term free piston mechanism is used herein and in the claims to mean all elements of a free piston gas generator except the fuel supply and combustion systems. Several different types of free piston mechanism are known as shown, for example, in references D, E, and F.